The present invention constitutes an improvement in the kind of apparatus disclosed in U.S. Pat. Nos. 3,809,286 and 3,874,566 and in U.S. Pat. No. 4,015,747. The subject matter of both patents and the application are incorporated herein by reference.
The prior patents and the prior application disclose apparatus in which the feeding or discharging of granular material from a mass thereof is effected and closely controlled by a special arrangement of a centrally apertured horizontal feed plate disposed below a shroud or baffle at least the lower end of which is located within the mass of material. The construction and disposition of the shroud and feed plate is such that the granular material does not flow spontaneously by gravity through the central feed aperture in the feed plate when the latter is stationary. However, in some situations the granular material does flow spontaneously to an extent into the periphery of the space directly below the shroud where it comes to rest in the form of an annular mass of material of which at least a portion resides on the upper surface of the plate. Thereafter, the plate is driven in an orbital path about a vertical axis with the result that granular material on the plate is carried inwardly with respect to the vertical axis of the shroud. As this occurs an additional quantity of material flows by gravity from the main mass into the space formerly occupied by the displaced quantity thereby preventing reverse displacement of the initially displaced quantity during continued orbital movement. In one form of the apparatus, the feed plate moves relative to the initially displaced material so that an edge portion of the feed aperture in the plate moves under this material which then passes through the aperture by gravity. The overall result is that granular material is continuously fed downwardly through the feed plate along a path which moves around the circumference of the feed aperture, the flow of material being proportional to the speed of the plate.
In another form of apparatus it is necessary for the feed plate to reach out beyond the periphery of the shroud in order for it to perform a proper feeding or discharging operation. This may be necessary, for example, if the granular material has little or no tendency to flow inwardly under the shroud. This condition may be present if the material is finely-divided and non-free-flowing as may be the case with especially cohesive or sticky substances. The condition may also result if the material contains lumps which are of large size relative to the vertical distance between the shroud and the feed plate. For example, some powders which are readily free-flowing once they are put in motion tend to form arches within the mass of powder when a portion of the material is removed by gravity through a feed or discharge aperture with the result that flow through the aperture will be intermittent or cease altogether. In the case of chunky material containing lumps of irregular size and shape, the material may wedge between the shroud and the feed plate and impede or prevent flow of the material.
In the preferred form of the apparatus there is provided a feed plate having a central feed aperture which is larger than a discharge aperture in a horizontal shelf or wall over which the feed plate is mounted. In this construction, orbital movement of the feed plate displaces the granular material inwardly toward its center in the manner described above but instead of falling by gravity through the feed aperture in the feed plate the material is first deposited on the shelf and is subsequently pushed over the edge of the discharge aperture in the latter by continued orbital movement of the feed plate. This arrangement permits a smaller area of contact between the lower surface of the feed plate and the shelf and thereby reduces friction at this location. The same is true with respect to reduced friction between the upper surface of the feed plate and the mass of granular material. In addition, the feed plate tends to remain buried by the granular material, and this is advantageous in protecting the feed plate from any corrosive atmosphere which may be present. This type of feed plate may have a diameter either greater or smaller than the shroud.
Orbital movement of a feed plate means that the plate moves in a generally circular path either with or without rotation about its own axis. When there is no rotation of the plate about its own axis, all points on the plate move in circular paths of the same radius which is small compared to the radius of the plate. When the plate also rotates about its own axis, the plate moves generally as if its circumference were rolling along the inside of a ring of slightly greater diameter than the plate. The form or location of the drive means employed to effect either type of movement is usually immaterial.
By granular material is meant any solid or semi-solid material in the form of discrete particles, grains or lumps without regard to size or density so long as the material can be made to flow downwardly by gravity when acted on by the feed plate. The term encompasses all types of finely divided material including ground cement, as well as larger particulate matter, such as sand, stone and coal.
With some materials such as coal it has been found that fine particles of the material tend to lodge between the lower surface of the feed plate and the upper surface of the bottom wall or shelf of the bin or other container. As the fine particles accumulate there is a tendency for the feed plate to be forced upwardly with the result that the drive connection between motor and the feed plate may bind. This accumulation is generally less likely to occur when the feed plate is free to roll about its own axis during its orbital movement. When little or no rolling movement is permitted the tendency is more pronounced. In any event periodic reversal of the direction of movement of the plate can often be employed to reduce or prevent the tendency of the feed plate to move upwardly. It has been found that this tendency is further reduced when the reversal feature is used for a feed plate which is provided with studs or other projections on its lower surface. In this construction it is thought that the particulate material packs between the studs and forms a scrubbing surface which tends to prevent further accumulation of particulate material. In any event the use of studs or their equivalent together with a periodic drive reversal in a machine where only partial rolling of the feed plate occurs has been found in many instances to prevent binding of the feed plate drive under operating conditions where binding did occur with a smooth feed plate operated in only one direction.
The problem of feed-plate binding has not been entirely solved however. Under some circumstances there is a tendency for the material to cause binding, even when a studded feed plate is periodically orbited in opposite directions.